The present disclosure relates to blood reservoirs for extracorporeal blood circuits. More particularly, it relates to blood reservoirs combining blood flows from a primary venous source and an auxiliary source and useful with various perfusion systems.
In many surgical procedures, the functions of the heart and lungs are performed outside the body by specialized devices, such as membrane oxygenators, cardiac assist pumps, and heat exchangers. This array of equipment is operated by a perfusionist who supervises the removal and return of the patient's blood during the surgical procedure. The patient's blood is stored in a venous reservoir, interposed between the vena cava tap and the pump of the heart-lung machine, which pumps the blood through the oxygenator and back into the patient's aorta. The venous reservoir also serves as a fluid buffer in the external circulation system to smooth out variations between the blood flow available from the vena cava and the demands of the heart-lung machine pump. Cardiotomy blood is also recovered, treated (e.g., filtration of surgical field debris), and returned to the patient. The venous blood and the cardiotomy blood can be separately maintained, or can be combined into a single, hard shell cardiotomy and venous reservoir.
Conventional cardiopulmonary bypass uses an extracorporeal blood or perfusion circuit that is coupled between the arterial and venous cannulae and includes a venous drainage or return line, a venous blood reservoir (or combination cardiotomy and venous blood reservoir), a blood pump, an oxygenator, an arterial filter, and blood transporting tubing or “lines”. It is necessary to minimize the introduction of air into blood in the extracorporeal blood circuit, and to remove any air that does accumulate before the filtered and oxygenated blood is returned to the patient to prevent injury. In this regard, a key parameter measured by clinicians is the count and volume of gaseous microemboli (GME). GME performance is used to characterize the efficacy of a disposable perfusion circuit, where lower GME volume translates into superior air handling ability.
There are several ways that air can be introduced into the perfusion circuit before or at the circuit's reservoir. For example, air can be introduced from the venous cannula due to physician error or case complications. Also, air can be introduced through suction devices that empty into inlets of the circuit reservoir. Along the same lines, air can be introduced into the blood by turbulent flow within the reservoir. Conventional perfusion circuits incorporate various components or component designs to remove this air. For example, the reservoir can be designed to accumulate and purge larger air bubbles. Also, filters can be added to the circuit and/or be incorporated into the reservoir itself for removing GME and other particles. Thus, air introduced through the cannula may be easily separated from the blood when it enters the reservoir by simply allowing the large bubbles to float to the surface of the reservoir and dissipate into the atmosphere. However, if the bubbles at or immediately before the reservoir from the cannula are broken up, for example, by turbulent flow or sharp edges, they will lose their buoyancy and have the risk of passing through the reservoir filtration media. As a point of reference, venous filtration media is typically sized between 38 microns and 150 microns. So long as the air from the venous cannula is larger than the venous filtration media size, there is a good chance the bubbles will not pass through the media. If the air does not pass through the venous filtration media, there will be good GME performance. If the air from the venous cannula is broken into small bubbles, there is a good chance the air will pass through the venous filtration media, resulting in poor GME performance.
With the above in mind, conventional perfusion reservoir devices (either a standalone venous reservoir or a combined cardiotomy and venous reservoir) employ a “downtube” fluidly connected to the venous cannula and emptying venous blood into a chamber of the reservoir for treatment by the venous filtration media. Due to the large number of fluid connections associated with most extracorporeal blood circuits, the reservoir will conventionally incorporate a plethora of additional inlet ports. To save on space, blood flow from one or more auxiliary circuit components are commonly merged with the venous blood flow through the downtube via a luer port formed directly with the downtube. For example, a continuous one-way purge line originating from the top of an arterial filter device is connected to the venous reservoir downtube (either directly or via a separate blood sampling manifold). By allowing a continuous flow of approximately 200 mL/minute to drain from the top of the arterial filter to the reservoir, it serves as an air purge from the arterial filter. This one-way purge line prevents the accidental injection of air into the systemic side of the circuit that might otherwise occur during blood sampling or drug injection. Blood flow from other circuit components, such as an oxygenator air purge, hemoconcentrator, etc., may also be connected to the reservoir downtube's luer port(s). Regardless, luer ports traditionally are placed on the reservoir downtube at a 90° angle. When blood flow through the luer port is directed or merged into the primary venous flow through the downtube, turbulent flow is created. In instances where the primary venous blood flow includes bubbles, this turbulent flow may break up the bubbles into smaller forms, leading to the potential concern described above.
In light of the above, a need exists for an extracorporeal blood circuit reservoir device configured to merge auxiliary blood flow with primary venous blood flow in a manner that does not induce turbulent flow.